1. Field of the Invention
The present invention relates to a pixel interpolation method to be adapted in digital cameras or the like.
2. Description of the Background Art
A CCD imaging device for use in digital cameras or the like photoelectrically transfers light received through a color filter to output pixel data. Such color filter includes an RGB color filter, a YMCK color filter and the like. Through a single-chip color filter, single-color pixel data is output per pixel. For instance, when employing the RGB color filter, pixel data having one of R (red), G (green) and B (blue) color components is output per pixel.
Therefore, in the case of pixel data output from a CCD imaging device equipped with a single-chip color filter, single-color image data is output per pixel, and thus image data of other color components is to be interpolated. Various algorithms are used in the interpolation.
However, the interpolation is an operation of estimating pixel data of a target pixel from pixel data of neighboring pixels around the target pixel, and accordingly, misinterpolation may be performed depending on the contents of an image. Therefore, there is a technique for improving the interpolation accuracy in which the difference between G signals in the vertical direction and the difference between G signals in the horizontal direction are calculated to obtain correlations in the vertical and horizontal directions, respectively, thereby performing pixel interpolation in accordance with the correlations.
Japanese Patent Application Laid-Open Nos. 5-153562 (1993), 2001-94951 and 2003-230109 disclose a technique for evaluating correlations in diagonal directions in addition to a correlation in the vertical direction to perform pixel interpolation.
The above method is to improve the accuracy in pixel interpolation by evaluating the correlations in diagonal directions, but is a mere extension of the interpolation method using correlations in the vertical and horizontal directions, which therefore may cause misinterpolation in some cases.